Articles containing nanofibers produced from low melt flow rate polymers

ABSTRACT

The present invention is directed to hygiene articles comprising nanofibers. The nanofibers are made from a melt film fibrillation process with a polymer composition having a melt flow rate of less than about 400 decigram per minute. The nanofibers, having a diameter of less than 1 micron, must comprise a significant number of the fibers in one layer of the web contained by the hygiene article. The hygiene articles include diapers, training pants, adult incontinence pads, catamenials products such as feminine care pads and pantiliners, tampons, personal cleansing articles, personal care articles, and personal care wipes including baby wipes, facial wipes, and feminine wipes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/483,730, filed Jun. 30, 2003.

FIELD OF THE INVENTION

The present invention relates to hygiene articles made from nanofibersand method of producing the nanofibers. The nanofibers are made from alow melt flow rate polymer composition.

BACKGROUND OF THE INVENTION

The need for articles produced from nonwoven containing nanofibers hascontinued to increase. The diameters of nanofibers are generallyunderstood to be less than about 1000 nanometer or one micron. Thenanofibers webs are desired due to their high surface area, low poresize, and other characteristics. The nanofibers, also commonly calledmicrofibers or very fine fibers, can be produced by a variety of methodsand from a variety of materials. Although several methods have beenused, there are drawbacks to each of the methods and producing costeffective nanofibers has been difficult. Therefore, hygiene articles andother disposable consumer products containing nanofibers have not beenmarketed.

Methods of producing nanofibers include a class of methods described bymelt fibrillation. Melt fibrillation is a general class of making fibersdefined in that one or more polymers are molten and extruded into manypossible configurations, such as co-extrusion, homogeneous orbicomponent films or filaments, and then fibrillated or fiberized intofibers. Nonlimiting examples of melt fibrillation methods include meltblowing, melt film fibrillation, and melt fiber bursting. Methods ofproducing nanofibers, not from melts, are film fibrillation,electro-spinning, and solution spinning. Other methods of producingnanofibers include spinning a larger diameter bicomponent fiber in anislands-in-the-sea, segmented pie, or other configuration where thefiber is further processed after the fiber has solidified so thatnanofibers result.

Melt blowing is a commonly used method of producing fibers. Typicalfiber diameters range from 2 to 8 micron. Melt blowing can be used tomake fibers with smaller diameters but with considerable changes neededto the process. Commonly, redesigned nozzles and dies are needed.Examples of these include U.S. Pat. Nos. 5,679,379 and 6,114,017 byFabbricante et al. and U.S. Pat. Nos. 5,260,003 and 5,114,631 by Nyssenet al. These methods utilize relatively high pressures, temperatures,and velocities to achieve the small fiber diameter.

Melt film fibrillation is another method to produce fibers. A melt filmtube is produced from the melt and then a fluid is used to formnanofibers from the film tube. Two examples of this method includeTorobin's U.S. Pat. Nos. 6,315,806; 5,183,670; and 4,536,361; andReneker's U.S. Pat. Nos. 6,382,526 and 6,520,425, assigned to theUniversity of Akron. Although these methods are similar by first forminga melt film tube before the nanofibers result, the processes usedifferent temperatures, flow rates, pressures, and equipment.

Film fibrillation is another method of producing nanofibers although notdesigned for the production of polymeric nanofibers to be used innonwoven webs. U.S. Pat. No. 6,110,588 by Perez et al., assigned to 3M,describes of method of imparting fluid energy to a surface of a highlyoriented, highly crystalline, melt-processed polymer film to formnanofibers. The films and fibers are useful for high strengthapplications such as reinforcement fibers' for polymers or cast buildingmaterials such as concrete.

Electrospinning is a commonly used method of producing nanofibers. Inthis method, a polymer is dissolved in a solvent and placed in a chambersealed at one end with a small opening in a necked down portion at theother end. A high voltage potential is then applied between the polymersolution and a collector near the open end of the chamber. Theproduction rates of this process are very slow and fibers are typicallyproduced in small quantities. Another spinning technique for producingnanofibers is solution or flash spinning which utilizes a solvent.

Two-step methods of producing nanofibers are also known. A two-stepmethod is defined as a method of forming fibers in which a second stepoccurs after the average temperature across the fiber is at atemperature significantly below the melting point temperature of thepolymer contained in the fiber. Typically, the fibers will be solidifiedor mostly solidified. The first step is to spin a larger diametermulticomponent fiber in an islands-in-the-sea, segmented pie, or otherconfiguration. The larger diameter multicomponent fiber is then split orthe sea is dissolved so that nanofibers result in the second step. Forexample, U.S. Pat. Nos. 5,290,626 by Nishio et al., assigned to Chisso,and 5,935,883, by Pike et al., assigned to Kimberly-Clark, describe theislands-in-the-sea and segmented pie methods respectively. Theseprocesses involve two sequential steps, making the fibers and dividingthe fibers.

To produce disposable hygiene articles containing nanofibers that arecommercially advantageous, the cost of the nanofibers must becontrolled. Equipment cost, process costs, any additional process aids,and polymer costs are all areas where costs can be controlled.Therefore, it is an object of the invention to produce nanofibers whichare low in cost.

SUMMARY OF THE INVENTION

The present invention is directed to hygiene articles comprisingnanofibers. The nanofibers are made from a melt film fibrillationprocess with a polymer composition having a melt flow rate of less thanabout 400 decigram per minute. The nanofibers, having a diameter of lessthan 1 micron, must comprise a significant number of the fibers in onelayer of the web contained by the hygiene article. The hygiene articlesinclude diapers, training pants, adult incontinence pads, catamenialsproducts such as feminine care pads and pantiliners, tampons, personalcleansing articles, personal care articles, and personal care wipesincluding baby wipes, facial wipes, and feminine wipes. The presentinvention is also directed to hygiene articles comprising a nonwoven webcomprising a layer having a significant number of nanofibers withdiameters less than one micron. The nanofibers are made from a polymercomposition having a melt flow rate of less than about 400 decigram perminute and using a melt film fibrillation process comprising the stepsof providing a polymer composition, utilizing a central fluid stream toform an elongated hollow polymeric film tube, and using a fluid to formmultiple nanofibers from the hollow tube.

DETAILED DESCRIPTION OF THE INVENTION

One way of reducing the cost of the nanofiber is by using low melt flowrate polymers which are more economical than high melt flow ratepolymers. Low melt flow rate polymers have a higher molecular weight andare more easily produced and therefore, more widely available.Typically, low melt flow rate polymers are stronger, less abrasive orlinting, and more stable. Therefore, an hygiene articles containingnanofibers produced from low melt flow rate polymers are desired for thepresent invention.

It has been found that to achieve lower fiber diameters, polymers withhigher melt flow rates are more commonly used than polymers with lowermelt flow rates. This is because the higher melt flow rate polymer isable to flow faster, attenuate more easily, and form smaller diameterfibers. High melt flow rate polymers and high attenuation energies, suchas high gas velocities, flow rates, and take up speeds, are used tocreate the nanofibers. Generally, all of these parameters must optimizedto form the nanofibers. Therefore, one having ordinary skill in the artwould not utilize a low melt flow rate polymers in a single step meltfibrillation process to form nanofibers. The present invention relatesto hygiene articles made from nanofibers. The nanofibers are producedfrom a polymer composition. The polymer composition is defined as one ormore thermoplastic polymers plus any additional ingredients. The polymercomposition of the present invention will have a melt flow rate of lessthan about 400 decigrams per minute. The melt flow rate is measuredusing ASTM method D-1238. Preferably, the melt flow rate is less thanabout 300 decigrams per minute, more preferably less than about 200decigrams per minute, and most preferably less than about 100 decigramsper minute. A most preferred range for melt flow rates is from about 1decigram per minute to about 100 decigrams per minute. Generally, thelower the melt flow rate the more preferred. Therefore, polymers withmelt flow rates less than about 50 decigrams per minute and 30 decigramsper minute are even more preferred.

Typically, polymers have relatively low flow rates but are combined withother materials, such as peroxide, to increase the melt flow rate. Thisis because many processes which make fibers, particularly nanofibers,cannot use low melt flow rate polymers. Preferably, the process of thepresent invention will produce a film which is thicker and/or has ahigher polymer content than single fibers. This film is than formed intonanofibers.

Suitable thermoplastic polymers include any polymer suitable for meltspinning and having a low melt flow rate. The rheological properties ofthe polymer as it is present in the die must be such that the low meltflow rate polymer can be melt extruded and is able to form a film. Themelting temperature of the polymer is generally from about 25° C. to400° C.

Nonlimiting examples of thermoplastic polymers which may have a meltflow rate below about 400 decigram per minute include polyolefins,polyesters, polyamides, polyurethanes, polystyrenes, biodegradablepolymers including thermoplastic starch, PHA, PLA, starch compositions,and combinations thereof. The homopolymer, copolymers, and blendsthereof are included within this description. The most preferredpolymers are polyolefins such as polypropylene, polyethylene, nylons,and polyethylene terphalate.

Optionally, the polymer may contain additional materials to provideadditional properties for the fiber. These may modify the physicalproperties of the resulting fiber such as elasticity, strength, thermalor chemical stability, appearance, absorbency, odor absorbency, surfaceproperties, and printability, among others. A suitable hydrophilic meltadditive may be added. Optional materials may be present up to 50% ofthe total polymer composition as long as the melt flow rate of thepolymer composition is still within the identified range.

The fibers may be single or multicomponent fibers such as bicomponentfibers. The fibers may have a sheath-core or side-by-side or othersuitable geometric configuration. After the fibers are made, the fibersmay be treated or coated before formed into a web. Additionally, after aweb is made, the web may be treated. Optionally, additives may becompounded into the polymer resin and these additives may move out tothe surface of the fiber after the fibers are formed. The additives thatmigrate to the surface may need to be cured utilizing external energy,such as heat, or additives on surface may need to be chemically reactedwith another component or curing may need to be catalyzed in thepresence of another component, such that additional components may beadded to the process while the fibers are being made or after the fibersare made using the resin with additives. Suitable treatments includehydrophilic or hydrophobic treatments. An example of hydrophobictreatment is poly-di-methyl-siloxanes. The specific treatment depends onthe use of the web, type of polymer, and other factors.

The method of making the nanofibers of the present invention is any onestep melt film fibrillation process that can utilize a thermoplasticpolymer composition having a melt flow rate of less than about 400decigram per minute. Melt fibrillation processes are defined as aprocess utilizing a single phase polymer melt wherein fibers are formed.Single phases can include a dispersion but does not included solventbased melts such as those used in solution or electrospinning. Typicalsingle step melt fibrillation processes include melt blowing, melt filmfibrillation, spunbonding, melt spinning in a typical spin/draw process,and combination thereof. Single step processes do not include two-stepprocesses where a larger fiber is first made and then split aftersolidification by removing part of the fiber or separating it. Theprocess must be suitable for utilizing a thermoplastic polymer having amelt flow rate of less than about 400 decigrams per minute and producingfibers having a diameter of less than about 1 micron.

The method of producing nanofibers by melt film fibrillation processgenerally involves providing a polymeric melt, utilizing a central fluidstream to form an elongated hollow polymeric film tube, and then usingair to form multiple nanofibers from the hollow tube. Suitable methodsare detailed, for example, in U.S. Pat. No. 4,536,361 to Torobin andU.S. Pat. Nos. 6,382,526 and 5,520,425 to Reneker. The melt fibrillationmethods can utilize different processing conditions. Reneker's methodmore specifically includes the steps of feeding the polymer into anannular column and forming a film or tube at the exit of the annularcolumn where a gas jet space is formed. A gas column then providespressures on the inner circumference of the polymer tube. When thepolymer tube exits the gas jet space, it is blown apart into many smallfibers, including nanofibers, due to the expanding central gas.

An example of a melt film fibrillation method more specifically includesthe steps of melting the polymer to form a polymeric melt. The polymericmelt will contain the polymer composition and any other ingredients. Thepolymeric melt is extruded through an orifice which in turn contains acentral fluid stream such that the polymer extrudes as an elongatedhollow tube. The orifice may be part of a nozzle. It is obvious to thoseskilled in the art that the overall design of the nozzle may have to beoptimized for process stability. Furthermore, the central fluid streammay be concentric or eccentric. A fiberizing fluid, such as a centralfluid stream, is blown to form an elongated hollow tube. The fiberizingfluid will then provide pressure on the inner surface of the elongatedhollow tube. Thinned wall or weakened portions may form in the hollowtube to more easily and controllably enable the formation of fibers,including nanofibers. The weakened portions may result from notches orprojections located on the outer surface of the central fluid jet tubeor on the inner surface of the polymer extrusion orifice. The elongatedhollow polymeric film tube is then subjected to a fluid to form thenanofibers. This fluid can be the central fluid stream or an entrainingfluid or any fluid stream to induce a pulsating or fluctuating pressurefield and forms a multiplicity of fibers, including nanofibers. Ifadvantageous, a nozzle providing cooling or heating fluid to the formednanofibers may be used.

The polymer is typically heated until it forms a liquid and flowseasily. The melted polymer may be at a temperature of from about 0° C.to about 400° C., preferably from about 10° C. to about 300° C., andmore preferably from about 20° C. to about 220° C. The temperature ofthe polymer depends on the melting point of the polymer or polymercomposition. The temperature of the polymer is less than about 50° C.above its melting point, preferably less than 25° C. above its meltingpoint, more preferably less than 15° C. above its melting point, andjust at or above its melting point or melting range. The melting pointor range is measured using ISO 3146 method. The melted polymer willtypically have a viscosity of from about 1 Pa-s to about 1000 Pa-s,typically from about 2 to about 200 Pa-s and more commonly from about 4to about 100 Pa-s. These viscosities are given over a shear rate rangingfrom about 100 to about 100,000 per second. The melted polymer is at apressure of about atmospheric pressure or slightly elevated.

The elongated hollow polymer tube can be circular, elliptical,irregular, or any other shape which has a hollow region. In some cases,the elongated hollow polymer tube may collapse immediately afterforming. In the case of the collapsed tube, it may be preferred to havethinned walls or weakened portions in the tube to aid in thefibrillation. Non-limiting examples of the fiberizing fluid are gasessuch as nitrogen or more preferably air. The fiberizing fluid istypically at a temperature close to the temperature of the meltedpolymer. The fiberizing fluid temperature may be a higher temperaturethan the melted polymer to help in the flow of the polymer and theformation of the hollow tube. Alternatively, the fiberizing fluidtemperature can be below the melted polymer temperature to assist in theformation and solidification of the nanofibers. Preferably thefiberizing fluid temperature is less than the polymer melting point,more preferably more than 50° C. below the polymer melting point, morepreferably more than 100° C. below the polymer melting point, or just atambient temperature. The pressure of the fiberizing fluid is sufficientto fibrillate the nanofibers and can be slightly above the pressure ofthe melted polymer as it is extruded out of the orifice.

The fiberizing fluid may have a velocity of less than about 500 meterper second. Preferably, the fiberizing fluid velocity will be less thanabout 100 meter per second, more preferably less than about 60 meter persecond, and most preferably from about 10 to about 50 meters per second.The fiberizing fluid may pulsate or may be a steady flow. Although it iscritical that this fiberizing fluid is present to aid in the formationof the elongated hollow polymeric film tube, the amount of fluid in thisstream may be very low.

The polymer throughput will primarily depend upon the specific polymerused, the nozzle design, and the temperature and pressure of thepolymer. The polymer throughput will be more than about 1 gram perminute per orifice. Preferably, the polymer throughput will be more thanabout 10 gram per minute per orifice and more preferably greater thanabout 20 gram per minute per orifice. There will likely be severalorifices operating at one time which increases the total productionthroughput. The throughput, along with pressure, temperature; andvelocity, are measured at the die orifice exit.

The fibrillation and solidification of the fibers may occur before thefibers and fluid exit the orifice. Once the elongated hollow tube exitsthe orifice, the nanofibers are formed. Commonly, the formation ofnanofibers occurs immediately upon exiting the orifice. One or morefluid streams are used to form the multiplicity of nanofibers. The fluidstream can be the central fluid stream, an entraining fluid, or anyother fluid stream. An entraining fluid can be used to induce apulsating or fluctuating pressure field to help in forming amultiplicity of nanofibers. The entraining fluid may be provided by atransverse jet which is located to direct the flow of entraining fluidover and around the hollow elongated tube and nanofiber forming region.The entraining fluid can have a low velocity or a high velocity, such asnear sonic or super sonic speeds. An entraining fluid with a lowvelocity will typically have a velocity of from about 1 to about 100meter per second and preferably from about 3 to about 50 meter persecond. The temperature of the entraining fluid can be the same as theabove fiberizing fluid, ambient temperature, or a higher temperature, ora temperature below ambient.

An additional fluid stream, a quench or heating fluid, can also be used.This additional fluid stream is located to direct fluid into thenanofibers to cool or heat the fibers. If the additional fluid is usedas a quenching fluid, it is at a temperature of from about −50° C. toabout 100° C. and preferably from about 10° C. to 40° C. If theadditional fluid is used as a heating fluid, it is at a temperature offrom about 40° C. to 400° C. and typically from about 100° C. to about250° C. Any fluid stream may contribute to the fiberization of thepolymer melt and can thus generally be called fiberizing fluids.

Any of the fluid streams, including the central fluid stream, anentraining fluid, or additional fluid stream, may contain a treatment,additive, coating, or other substance or particulate for changing thesurface, chemical, physical, or mechanical properties of the fibersproduced.

The nanofibers are laid down on a collector to form a web. The collectoris typically a conveyor belt or a drum. The collector is preferablyporous and vacuum may be applied to provide suction to aid fiber laydown on the collector. The distance from the orifice to the collectordistance, commonly called die-to-collector distance (DCD), can beoptimized for desired web properties. To reduce the amount of fiberbundling or roping, the DCD should be relatively low. This lowerdistance does not enable the fibers to have time to entangle, wraparound one another, or bundle. It may be desired to utilize more thanone DCD used in a web, to change the DCD during production, or to havedifferent beams with different DCDs. It may be desirable to form a webwith different uniformities by changing the DCD.

After the elongated hollow film tube is formed, the tube or thenanofibers may alternatively be subject to an additional process thatfurther promotes the formation of nanofibers. The further processingwould occur immediately after formation of the elongated hollowpolymeric film tube and before the nanofibers have solidified to stillbe considered a single step process. The additional processing canutilize one or more Laval nozzles to speed up the gas velocities tosonic and/or supersonic range. When polymer melt is exposed to such highgas velocities, it bursts into multiplicity of fine fibers. Examples ofa Laval nozzle are described in Nyssen et al., U.S. Pat. No. 5,075,161,in which a method of bursting polyphenylene sulfide melt into finefilaments is disclosed. The Laval nozzle may be positioned just afterthe spinning nozzle when the elongated hollow polymeric film tube isproduced. Alternatively, Laval nozzle could be positioned just after thenanofibers have formed to further reduce the fiber size. Polymer fiberscan be produced by subjecting the polymer melt streams to drawing outand cooling to below the melt temperature by extruding them into agaseous medium which flows essentially parallel to the polymer meltstreams and attains sonic or supersonic speed. This simultaneousdeformation and cooling gives rise to amorphous fine or extremely finefibers of finite length. High speed fiber bursting minimizes the surfaceoxidation of the fibers. The spinning speed, melt temperature, and theposition of the Laval nozzle are appropriately set to achieve onlypartial thermal oxidation of fine filaments at their surface.

Various processes and combination of processes can be used to make thewebs of the present invention. Melt fiber bursting, as disclosed in WO04/020722 by Sodemann et al., can be combined with melt filmfibrillation of the present invention on two separate beams on a singleline. Various aspects of melt fiber bursting can be incorporated intomelt film fibrillation, such as producing fibers of different strengthsand diameters to provide a desired combination of properties.Alternatively, aspects of melt film fibrillation can be included inother melt fibrillation processes to increase the throughput rate byutilizing a hollow elongated tube to form fibers. For example, the meltfilm fibrillation process of the present invention could be modified toinclude a Laval nozzle to aid in drawing down the fibers. Drawing downcan aid in further attenuation and increase the strength of the fibers.This may be particularly preferred for high Tg polymers such aspolyesters in which stress-induced crystallization happens at speeds inexcess of 4000 m/min.

The nanofibers of the present invention are used to make nonwoven webs.The web is defined as the total nonwoven composite. A web may have oneor several layers. A layer is the web or part of a web that is producedin a separate fiber lay down or forming step. The webs of the presentinvention will comprise one or more layers having a significant numberof nanofibers having diameters of less than one micron. A significantnumber is defined as at least about 25%. The significant number offibers can be at least about 35%, at least about 50%, or more than 75%of the total number of fibers in the layer. The web could have 100% ofthe fibers having a diameter of less than about one micron. The fiberdiameters of the web are measured using a scanning electron microscopeat a magnification of greater than about 500 times and up to about10,000 times as needed for visual analysis. To determine if asignificant number of fibers have diameters less than one micron, atleast about 100 fibers and preferably more fibers must be measured. Themeasurements must occur at various regions throughout the layer.Sufficient sampling that is statistically significant must occur.

The fiber diameter of the remaining larger fibers, up to 75%, may havefiber diameters in any range. Typically, the larger fiber diameters willbe just above one micron to about 10 microns.

Preferably, a significant number of fibers in a layer will have a fiberdiameter of less than about 900 nanometer and more preferably from about100 nanometers to about 900 nanofibers. The fibers may have a diameterof less than 700 nanometers and from about 300 to about 900 nanometers.The preferred diameters depend upon the desired use of the web. Forprocess and product benefits, it may be desirable in some applicationsto have a significant number of fibers having a diameter of less thanabout one micron and a significant number of fibers having a diameter ofgreater than about one micron. The larger fibers may trap and immobilizethe nanofibers. This may help to reduce the amount of clumping or ropingof the nanofibers and prevents the nanofibers from being carried off bystray air currents.

The layers of nanofibers in a web of the present invention may containmore than one polymer. Different polymers or polymer blends may be usedfor different orifices to produce layers in a web having different fiberdiameters and different polymer compositions.

It may be desirable to produce a single layer nonwoven with varyingfiber diameters. Alternatively, it can be desired to produce a nonwovenweb with multiple layers with each layer having different fiberdiameters. The melt film fibrillation process can be modified to produceboth small and large diameter fibers to make various webs. The smallerfiber diameters are referred to as having a significant number of fibershaving a diameter of less than one micron. The larger diameter fibersinclude fibers from the melt blowing range (typically 3 to 5 microns) tothe spunbond (typically around 15 microns) or any range of fiberdiameters above 1 micron. For example, one layer can be produced with anaverage fiber diameter of less than one micron and another layer with anaverage fiber diameter of around 5 microns. This type of structure couldbe used where traditionally SMS webs are used. Another example is toproduce a nanofiber web with multiple layers, with each layer having adistinct average fiber diameter such as one layer having an averagefiber diameter of 0.4 micron and a second layer having an average fiberdiameter of 0.8 micron. The webs with various fiber diameters can beproduced on the same line with the same equipment. This is aninexpensive way as the same equipment and components can be used. Theoperating costs and equipment costs are both controlled. Also, ifdesired, the same polymer can be used to produce different fiberdiameters.

It may be desired to form a web of several layers. The nanofiber layermay be combined with one, two or more layers. Aspunbond-nanofiber-spunbond web is one example. Basis weights for thetotal composite webs range from about 5 gsm to about 100, preferablyfrom about 10 to about 100 gsm, and more preferably from about 10 gsm toabout 50 gsm. For use as a barrier layers, the total composite web basisweight may be from about 10 gsm to about 30 gsm. The basis weight ofonly the nanofiber layer is from about 0.5 gsm to about 30 gsm andpreferably from about 1 gsm to about 15 gsm.

After the nonwoven is made, it may be subject to post processing.Nonlimiting examples of post processing include solid state formation,consolidation, lamination, surface coating, corona and plasma treatment,dyeing, and printing. Nonlimiting examples of solid state formationinclude processes using intermeshing rolls, such as in U.S. Pat. No.5,518,801 and referred to in subsequent patent literature as “SELF”webs, which stands for “Structural Elastic-like Film”, texturing,stretching, aperturing, laminating, local straining, micro creping,hydroforming, and vacuum forming. Nonlimiting examples of consolidationinclude thermal bonding, through air bonding, adhesive bonding, andhydroentangling.

The hygiene articles of the present invention will contain the abovedescribed nonwoven webs. The web may comprise the entire hygienearticles, such as a wipe, or the web may comprise one component of thehygiene article, such as a diaper. The hygiene articles include diapers,training pants, adult incontinence pads, catamenials products such asfeminine care pads and pantiliners, tampons, personal cleansingarticles, personal care articles, and hygiene wipes including babywipes, facial wipes, body wipes, and feminine wipes. Personal carearticles include articles such as wound dressings, active delivery wrapsor patches, and other substrates that are applied to the body,particularly the skin.

In a diaper, the web may be used as a barrier layer or an outercover.The webs may also be used as a high barrier cuff with a high hydrostatichead to enable low leakage incident rates of thin, narrow crotch diapersdesired for comfort and fit. The webs may be used in wipes to enableimproved lotion handling and reduced gradient of liquids. The webs mayalso provide controlled delivery of a substance. The delivered substancecan be of liquids, lotions, actives, or other materials. Due to the highsurface area of the nanofibers, the webs may be used as absorbentmaterials for wipes or cores of feminine care product pads, diapers,training pants, or adult incontinence. The webs may provide enhanceddistribution of fluids and/or retention. Additionally, the webs forabsorbent uses may be made with added particulates or absorbent ornatural fibers for increased absorbance or certain layers of the websmay have different properties. The nanofiber webs may also be used inarticles wherein opaqueness is desired. Added opaqueness may result dueto the small fiber diameter and uniformity; or pigments may be added tothe polymer melt or webs. Commonly, the nanofiber layer is combined in aweb with a spunbond layer. There may be one spunbond layer or a spunbondlayer on each side of the nanofiber web.

In a diaper or other disposable absorbent product, the nonwoven webcontaining nanofibers may be utilized as a barrier layer. The barrierlayer may be disposed between an absorbent core and an outer layer ofthe disposable absorbent product. The absorbent core is the component ofthe article that is primarily responsible for fluid handling propertiessuch as acquiring, transporting, distributing, and storing body fluids.The absorbent core is typically located between a liquid perviousbody-side inner layer and a vapor permeable, liquid impermeable outercover. The outer layer, also known as the back sheet or outer covering,is located on the outside of the disposable product. In the case of adiaper, the outer layer contact the user's garment or clothing. Thebarrier layer may alternatively or also be disposed between theabsorbent core and an inner layer. The inner layer, also known as a topsheet, is located on the side closest to the user's skin. The innerlayer may contact the user's skin or may contact a separate top sheetwith contacts the user's skin. The barrier layer may be absorbent. Thenonwoven web may comprise the layer around the absorbent core and helpto distribute or handle fluids. The nonwoven web may be a fluiddistribution layer, which may be located adjacent to the core. Thebarrier layer most preferably has a balance between convective air flowand absorptive barrier property. The convective air flow property iseffective to reduce the relative humidity within the space between theabsorbent article and the wearer's skin. The combination of liquidabsorption and liquid barrier property provides protection against thewet through problem and is especially beneficial when the absorbentarticle is under impact and/or sustained pressure. Further descriptionand benefits of the barrier layers may be found in WO 01/97731.

The webs may be used to make hygiene wipes that are dry orpre-moistened. The nanofiber may be used in wipes to enable improvedlotion handling and reduced gradient of liquids. The nanofiber layer mayprovide a partial barrier and may be partially or completely liquidimpervious. The webs may also provide controlled delivery of a substanceor active such as a drug. The delivered substance can be liquids,lotions, enzymes, catalysts, actives, or other materials such asemollients, surfactants, wetting agents, polishes, oils, organic andinorganic solvents, pastes, gels, pigments, or dyes. The webs mayprovide enhanced distribution of fluids and/or retention. Additionally,the webs for absorbent uses may be made with added particulates orabsorbent or natural fibers for increased absorbance or certain layersof the webs may have different properties. The nanofibers may beproduced to be low density or porous nanofibers. The nanofibers may beproduced with an inflatent or blowing agent.

Due to the high surface area of the nanofibers, the webs may be used asabsorbent materials for wipes or cores of feminine care product pads,diapers, training pants, or adult incontinence. The high surface areaalso enhances cleaning and may be used in hygiene cleaning wipes. Thewebs may provide enhanced distribution of fluids and/or retention.Additionally, the webs for absorbent uses may be made with addedparticulates or absorbent or natural fibers for increased absorbance orcertain layers of the webs may have different properties.

The nanofiber webs may also be used in articles wherein opaqueness isdesired. Added opaqueness may result due to the small fiber diameter anduniformity; or pigments may be added to the polymer melt or webs. Thewebs may also be low linting resulting from longer length fibers orentangling of fibers in the web. The tensile strength of the nanofiberwebs of the present invention can be greater than the tensile strengthof webs with similar fiber diameters and similar basis weights made fromother processes. The nanofiber webs of the present invention will besoft and may be softer than other webs with the same performance.

Other products that will benefit from a nanofiber web include a personalfilter or mask such as a surgical mask. Other medical uses of webscontaining nanofiber layers include surgical gowns, wound dressings, andmedical barriers.

The fiber diameter can be measured using a Scanning ElectronicMicroscope (SEM) and image analysis software. A magnification of 500 to10,000 is chosen such that the fibers are suitably enlarged formeasurements. Image analysis software for automatic sampling of fiberdiameter in the SEM picture is possible, but also a more manualprocedure can be used. In general, the edge of a randomly selected fiberis sought and then measured across the width (perpendicular to fiberdirection at that spot) to the opposite edge of the fiber. A scaled andcalibrated image analysis tool provides the scaling to get the actualreading in mm or micrometers (μm). Several fibers are randomly selectedacross the sample of web in the SEM. Typically, several samples from aweb are cut and tested in this manner and at least about 100measurements are made and all data are recorded for statistic analysis.If the result is to be recorded in denier, then the followingcalculation needs to be made. Diameter in denier=Cross-sectionalarea*density*9000 m*1000 g/kg. The cross-sectional area is ediameter²/4.The density for PP, e.g., can be taken as 910 kg/m³. To obtain decitex(dtex), the 9000 m is replaced by 10,000 m.

Basis weight can be measured consistent with compendial methods ASTM D756, ISO 536 and EDANA ERT-40.3-90. Basis weight is defined as mass perunit area, with grams per square meter (gsm) as the preferred unit.Required instruments are a scissors or a die-cutter for sample cuttingand an accurate weighing device, such as a scale. A sample is cut to atotal area of 100 cm² per layer with an accuracy and precision of ±0.5%.A scale or balance is needed with 0.001 g sensitivity, readable,calibrated and accurate to within 0.25% of the applied load. The samplesare conditioned at 23° Celsius (±2° C.) and at a relative humidity ofabout 50% for 2 hours to reach equilibrium. Weigh the cut sample with 10plies from the sample area for a total of 1000 cm²=0.1 m² on ananalytical balance to the nearest 0.001 g and record the weight. (Forsamples thicker than 1 mm, weighing only 1 ply is preferred but shouldbe noted.) Calculate the basis weight by dividing the weight by thesample area (all layers tested) to give the basis weight in gsm. Alldata are recorded for statistic analysis.

Web uniformity can be measured through several methods. Examples ofuniformity metrics include low coefficient of variation of porediameter, basis weight, air permeability, and/or opacity. Uniformityalso requires lack of fiber bundles or roping, or visible holes, orother such defects. Uniformity can be controlled by process modificationsuch as reducing the nozzle to collector distance. The reduction in thisdistance reduces the fiber bundling or roping and can provide moreuniform webs.

Pore diameter can be determined by methods known to those skilled in theart. The mean pore diameter is preferably less than about 15 microns,more preferably less than about 10 microns, and most preferably lessthan about 5 microns. The desired coefficient of variation for a uniformweb is less than 20%, preferably less than about 15%, and morepreferably about 10% or less. The lack of roping can be measured bycounting the number of ropes or bundles of fibers in a measured area ofthe web. The lack of holes is also measured the number of holes having adiameter above a certain threshold in a measured area of the web. Theholes may be counted if they are visible to the naked eye or are morethan 100 microns in diameter.

All documents cited are, in relevant part, incorporated herein byreference; the citation of any document is not to be construed as anadmission that it is prior art with respect to the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A hygiene article comprising a nonwoven web comprising a layer havingat least 50% nanofibers with diameters less than one micron and a meanpore diameter of less than about 15 microns, wherein said nanofiberscomprise a biodegradable polymer composition comprising a thermoplasticpolymer selected from the group consisting essentially of PLA, PHA,thermoplastic starch, and combinations thereof, wherein the polymercomposition has a melt flow rate of less than about 400 decigram perminute, and the nanofibers are the product of a single step meltfibrillation process.
 2. The hygiene article of claim 1 wherein thelayer comprises at least about 75% of nanofibers having a diameter ofless than one micron.
 3. The hygiene article of claim 1 wherein thepolymer composition has a melt flow rate of less than 200 decigram perminute.
 4. The hygiene article of claim 1 wherein the polymercomposition has a melt flow rate of less than 100 decigram per minute.5. The hygiene article of claim 1 wherein said thermoplastic polymerconsists essentially of PLA.
 6. The hygiene article of claim 1 whereinsaid thermoplastic polymer consists essentially of PHA.
 7. The hygienearticle according to claim 1 wherein said thermoplastic polymer consistsessentially of thermoplastic starch.
 8. The hygiene article of claim 1wherein the nonwoven web also comprises one or more layers of spunbondfibers.
 9. The hygiene article of claim 8 wherein the nonwoven web has abasis weight of from about 10 to about 100 gsm.
 10. The hygiene articleof claim 1 wherein the nanofiber layer of the nonwoven web has a basisweight of from about 0.5 gsm to about 30 gsm.
 11. The hygiene articleaccording to claim 1 wherein the hygiene article is selected from thegroup consisting of diapers, training pants, adult incontinence pads,catamenials products such as feminine care pads and pantiliners,tampons, personal cleansing articles, personal care articles, andpersonal care wipes such as baby wipes, facial wipes, and femininewipes, and combinations thereof.
 12. The hygiene article according toclaim 1 wherein the layer comprises two or more pluralities of fiberdiameter distributions wherein at least one plurality has a fiberdiameter of less than about one micron.